Thermo-mechanical analysis of irradiation swelling and design optimization of the IFMIF target assembly with bayonet backplate

The availability of a high flux neutron source for testing candidate materials under irradiation conditions, which will be typically encountered in future fusion power reactors (ITER, DEMO, FPR), is a fundamental step towards the development of fusion energy. To this purpose, the International Fusion Materials Irradiation Facility (IFMIF) represents the reference option to provide the fusion community with a DEMO-relevant neutron source capable of irradiating samples at a damage rate of up to 20 dpa/fpy (in steel) in a volume of 0.5 l. In the framework of the engineering design activities of IFMIF, ENEA is committed in the design of the lithium target assembly (TA) with removable (bayonet) backplate (BP) whose development has recently progressed up to a well advanced stage. However, an optimization of the system is still to be accomplished. In particular, the BP design needs to be revised in order to totally satisfy the ITER SDC-IC reference design criteria and fulfil the requirements on its lifetime which is limited by the neutron-induced swelling effects. In this work, a full thermo-mechanical analysis of the whole TA including a pseudo-transient simulation of the swelling effects in the BP over one year of full power operation has been performed by means of a 3D finite element (FE) model implemented through the quoted ABAQUS v. 6.14 code. A detailed neutronic analysis has been also performed by ENEA using the MCNP code to obtain the prompt nuclear responses, in terms of DPA and volumetric density of deposited nuclear heat power, to be used as input for the thermo-mechanical calculations. A new BP design capable to verify the SDC-IC design criteria and ensure its required swelling lifetime is proposed and described on the basis of the results of the performed analysis.